Model-driven design of geo-information services

This thesis presents a method for the development of distributed geo-information systems. The method is organised around the design principles of modularity, reuse and replaceability. The method enables the modelling of both behavioural and informational aspects of geo-information systems in an integrated way. This thesis introduces the concept of Geo-Information Service Infrastructure (GSI). The GSI concept adheres to the characteristics and needs of modern geo-information processing. The GSI builds on the existing principles for data sharing of the Geospatial Data Infrastructure concept. The term GSI is used to refer to a type of geo-information provision system from which specialised information products and services can be obtained by exploiting the elementary services (resources, processes and data) of a set of collaborating geo-service providers. This thesis presents a supporting architecture for the deployment of GSI services. An important idea underlying a GSI system is that services available in an information infrastructure should be composable. The method presented in this thesis is used to describe these elementary services and their interfaces, such that they can be accessed, combined and managed to create compound required services. These later services are defined to handle elaborated and specialised geo-processing tasks. Services are specified according to two perspectives namely the external perspective and the internal perspective. The external perspective specifies the observable behaviour of a service. This specification is used by designers for the development of the internal perspective and for the assessment of the resulting internal specification. A service specification according to the external perspective also provides potential users with a description of the service functionality and its interfacing mechanisms. The internal perspective describes internal structure of a required service in terms of compositions of simpler or more elementary services. This internal structure is defined in terms of architectural elements. Three types of architectural elements are distinguished, viz. data elements, processing elements and connecting elements. The data elements represent the information that is used, manipulated and/or generated by the system. The process element represent the geo-processing capabilities of the system, which can perform transformations on data elements. The connecting elements or mediators coordinate the interactions between the other architectural elements, and provide an interface to the service user. All specifications, accoriding to both the external and internal perspectives, are defined using ISDL (Interaction System Design Language) concepts. At the centre of a GSI system lies the repository service. The repository allows to organise the creation, updating, validation, accessing and sharing of service models and service instances. We emphasise the use of models as the mechanism to disclose information about services and to design more elaborated services out of combinations of existing elementary services. The repository is defined according to a metamodel on which all service models are based. The metamodel is used here to define a set of design concepts and their relationships, which one can use to produce models according to the GSI specific objectives. This thesis introduces and motivates the so-called mediator pattern to be used to structure compositions of architectural elements. This results in the organisation of a set of services into a behaviour definition that has a single coordinating element. One of the benefits of this approach is that it makes the service realisation accountable for the user. Another benefit is that it facilitates the use of workflow languages to implement the mediator behaviour, which choreographs the use of third-party services.